How accurate are the conception indicators on the digital tests?

[babiesbabies]

My best friend has recently had an early scan at 9 weeks but discovered she is in fact only 7 weeks (a heartbeat was detected. She does have irregular periods so it is possible that she conceived later thn thought. When she first found out she was pregnant she was using the first response digital tests and by their results she should be 2 weeks further along than the scan suggests. How accurate are these scans and should she be worried?

TIA

Hi. Had exactly the same with these tests. Went for my scan expecting to be 13 weeks and was only 11+2. My cycle is also irregular although I am still pretty sure my dates are correct. The midwife and my own research tell me that up until 12 weeks fetus development is at more or less the same rate in every pregnancy and after 12 weeks the scans become far less reliable for dating. At 7 weeks the fetus is very small, has a recognisable heartbeat and is only 1cm long approx. There is a big difference in development at later stages. I should tell your friend not to worry and look forward to seeing her baby at her 12 week scan. Hope all is well.x

Thanks.